1. Field of the Invention
This invention relates generally to apparatus and methods for object optimized rendering of computer generated page images into scan line raster data for driving a print engine.
2. Related Art
Prior to the advent of high quality computer generated page images, page images such as those found in newspapers, newsletters, magazines and the like were formed by graphic artists composing the page images by hand. Thus, each different type of object on a page image, including text, photographs, constant color areas or graphs such as pie charts, and sampled or continuously changing images such as sweeps, was optimally formed, independently of any other type of object.
Because these page images, comprising one or more of these types of objects, were composed by hand, each type of object was inherently treated independently of the other objects. Thus, the optimal halftone screen design for photographs, which differs from the optimal halftone screen-designs for constant color areas and text, could be optimally selected and the screen arranged to an optimal angle. Likewise, such optimal treatment of each type of object can be obtained.
With the advent of digital color workstations, copiers and printers, creators of page images who would previously have had to rely on graphic artists to compose and print their page images could instead create, compose and print them on their own using a computer connected to the digital color copier/printer.
However, such prior art digital systems for creating a page image, for decomposing the page image into print engine instructions, and for controlling the print engine treated a page image as a single, unitary image. Thus, in the page image shown in FIG. 1A (which is optimized for text), when a high frequency halftone screen is used, the text portion of the page image is quite sharp. However, the large square constant color portion of the page image contains an obvious mottling from printer noise. In addition, the sampled color portion and the sweep portion of the page image show obvious contouring due to the lack of sufficient gray levels available with the high frequency screen.
In the page image shown in FIG. 1B (which is optimized for the large constant color portion), a halftone screen specifically designed to hide printer instabilities produces a high-quality, text- and artifact-free constant color area. However, the sharpness of the text is decreased and the gray values for each tint are not well-related, so that the sampled color portion and the sweep portion are unacceptable. The sweep portion demonstrates that the gray levels do not step smoothly from one to the next, because each dot level is designed separately without relation to the other levels.
In the page image shown in FIG. 1C (which is optimized for sampled color and sweep portions), the sweep portion and the sampled color portion show higher quality because a low frequency halftone screen is used, with more gray levels available. However, the text is shown in low quality and the constant color portion shows an obvious texturing.
Accordingly, as shown in FIGS. 1A-1C, in the prior art systems, which treated each page image as a single bitmap or bytemap image, optimizing the image for any one type of object required the image quality of the other types of objects to be compromised. This is also shown in FIGS. 1D and 1E, which show a radial sweep with text superimposed on top of the radial sweep. In FIG. 1D, both the text and the background sweep are printed using a high frequency halftone screen. While the text in FIG. 1D is shown in high quality, the background sweep has an obvious contouring artifact due to the low number of gray levels. In FIG. 1E, both the background sweep and the text are printed using a low frequency screen. While the background sweep is shown in high quality and without the contouring visible in FIG. 1D, the text is shown in very low quality and is essentially unreadable.
Accordingly, there is a need in the art for a digital color copier/printer and method for creating, decomposing and outputting a page image to a print engine which allows for the printing characteristics of individual objects to be optimized, as in the hand-composing graphic arts field, while simultaneously retaining the benefits and efficiencies available when creating a page image using a microcomputer.
Such page images are created using Page Description Languages (PDLs) such as PostScript(trademark), Interpress(trademark), Graphical Display Interfaces (GDIs), such as the one used with Windows(trademark), Printer Command Languages (PCLs) for controlling a print engine, such as the Hewlett-Packard Printer Command Language (PCL-5)(trademark), or the like.
Thus, this invention provides a printer controller apparatus and method for converting a page image defined using a PDL or the like into print data and printer control commands such that each type of object in the page image is optimally printed.
This invention also provides for a printer controller apparatus and method for processing the page image such that the objects of the page image are processed optimally based on their object type, including using optimal compression and decompression techniques for each object type.
This invention also provides for an object optimized printer control device and method which generates a plurality of xe2x80x9cmetabitxe2x80x9d information (i.e., information about how best to render each byte of print data) based on the object type of the various objects forming the page image and passes the metabit data to the image output terminal (IOT).
This invention further provides for an object optimized printer control device and a method which automatically determines the object type for each independent object of the page image.
This invention also provides for an object optimized printer control system and method which allows a creator of a page image using a page description language to explicitly override or adjust the automatically determined object types.
This invention also provides for an intermediate format file structure containing information for each object on the page that may be stored for later editing, transmission and printing by an object optimized printer control device and method.
This invention also provides for a different intermediate format file containing a plurality of data channels and a metabit information channel that each have been optimally compressed, that may be decompressed and printed in real time by an object optimized printer device such that each type of object in the page image is optimally printed.
This invention also provides for an object optimized IOT which can receive metabit information and use it to select from a plurality of simultaneous inputs, such as a synchronized input from the printer""s input scanner, so that a page image can be constructed in real time from multiple inputs as it is being printed.
This invention also provides for an object optimized printer control device and method which can receive input from a plurality of sources other than the PDL source and use metabit information to mix it in real time while outputting the mixed data to the IOT.
This invention also provides for an editing method for processing the page image which keeps object information so that it may be edited object by object at the printer, without the need to create a modified PDL and re-convert it. The edits thus made at the printer may further be recorded so that at a later time they may be made a permanent part of the document on the digital workstation which created the document.
This invention also provides for the ability to use special hardware and software modules to provide different object optimized rendering and compression techniques, with each resource module controlled by metabit information controlling the selection of the rendering or compression method, and with the resource modules either distributed through the printing system or concentrated in a single location. The rendering modules can include, but are not limited to, modules which do object optimized color space transformations, object optimized spatial filtering, object optimized tone reproduction curves, object optimized choking or spreading, object optimized halftoning and object optimized engine artifact suppression.
Finally, this invention also provides for an object optimized print measurement apparatus and method which can use metabit information and measured print data to provide a plurality of adjustments to the page processing apparatus so that each type of object in the page image continues to be optimally printed in a stable manner.
In a first embodiment of this invention, a page image described using a page description language (PDL) and stored as a series of commands in the PDL is input to an object optimizing electronic subsystem (OOESS). A PDL decomposition means decomposes the page image described in the PDL into a data structure representing the page image. In the data structure, information relating to independent image objects is retained, including the information relating to object types and other individual characteristics such as color, optimal color space, layer information and the like.
Once the PDL decomposition means converts the page image described using the page description language, the copier/printer, or more generally the image output terminal (IOT), command instruction generating means converts the data structure into a series of command instructions, color designations and metabit rendering instructions for each scan line of the page image. The metabits are either automatically generated by a metabit generating means which analyzes each object to determine its type, or are explicitly set by the page image creator during the creation of the PDL description of the page image. Once all of the command instructions, the color designations and the metabits are generated for each scan line of the page image, they are output to the IOT controller.
The IOT controller receives the command instructions, the color instructions and the metabits generated during the decomposition process. The IOT controller combines the constant color and sampled color data and sends it with the metabit data to the IOT.
In a first embodiment of the IOT, the IOT includes a pair of halftoned screen generators and a color space transformation circuit. The byte-wide color data and the metabits output from the IOT controller are input to the IOT. The metabits are used to determine which halftone screen generator will be used on the color data and which color transformation will be applied by the color space transformation circuit. Once the IOT has generated the raster data from the color data and the metabits, the raster data is output to the marking subsystem for forming the page image on an output sheet.
In a second embodiment of the IOT controller, the sample color data compression/decompression circuit, mask data compression/decompression circuit, constant color compression/decompression circuit and command data compression/decompression circuit are incorporated into the IOT controller between the bus interface and the integrated combiner. The compression/decompression circuits allow the various types of data in the data structure to be optimally compressed for transfer on the system bus to the IOT controller. In addition, in the second preferred embodiment of the IOT controller, a color space transformer is incorporated into the IOT controller. By incorporating the color space transformer onto the IOT controller, the color space transformation for different objects of the page image can be performed just before printing, yet can be optimized based on the object type. In addition, incorporating the color space transformer onto the IOT controller widens the range of IOTs which can be used with the system of this invention.
In a third preferred embodiment of the IOT controller, an alternate form for the compressor/decompressor circuits is used.
In a fourth preferred embodiment of the IOT controller, two color space transformers are used to generate the color data to be output to the IOT. In this way, four bytes of data, representing each of the four color layer separations C, Y, M, K can be output simultaneously. By outputting the color data for all four color layer separations simultaneously, higher page output for the IOT can be accomplished and a wider range of IOTs can be used with the system of this invention.
These and other features and advantages of the invention are described in or are apparent from the following detailed description of the preferred embodiments.